Re: Constraint to ensure value does NOT exist in another table?

From: Alban Hertroys <dalroi(at)solfertje(dot)student(dot)utwente(dot)nl>
To: Mike Christensen <mike(at)kitchenpc(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Constraint to ensure value does NOT exist in another table?
Date: 2011-06-16 18:21:08
Message-ID: 7A6AE531-2041-4323-A253-1B006ACEB0A1@solfertje.student.utwente.nl
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On 16 Jun 2011, at 7:04, Mike Christensen wrote:

> I know I can setup a FK constraint to make sure Table1.ColA exists in
> Table2.Key, however what if I want to do the reverse?
>
> I want to ensure Table1.ColA does NOT exist in Table2.Key.. Can I do
> this with any sort of CHECK constraint, trigger, custom function, etc?
> Thanks!

Perhaps it's possible to use a unique constraint in a third table to guarantee those foreign keys can never have the same value. That would probably be more efficient than executing stored procedure code.

Alban Hertroys

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